Various types of metals and metal oxides are widely used as a general electrode and wire material having a fine multilayer structure in a semiconductor device, a liquid crystal display or the like. Wet etching methods using chemicals as well as dry etching methods, such as ion etching methods and plasma etching methods, are mainly known as conventional fine processing technologies for electrodes and wires using these metals or metal oxides. Different methods from among these methods are selected depending on the type of the metal, the metal oxide or a composite material of these, which is the object of etching, the targeted precision in the fine processing, the manufacturing method and the like.
Wet etching methods do not require an expensive apparatus in comparison with dry etching methods and are economical because only inexpensive chemicals are used. In addition, the effects of the wet etching methods are not affected by the form of the object of etching, and thus, wet etching methods are appropriate for etching an object having a three dimensional structure. Furthermore, metals which are dissolved in the etchant as a result of etching and useful as the electrode and the wire materials can be collected relatively easily from the etchant after use (etching waste), and therefore, wet etching methods are widely adopted from the point of view of effectively using natural resources.
A variety of metals, alloys of these and metal oxides are used as the above described electrode and wire materials for a semiconductor device or a liquid crystal display. Aluminum, molybdenum, titanium, tungsten, zirconia, tantalum, gold, silver, copper and alloys of these metals, for example, can be used as the metal.
Here, as the etchant for tungsten films made of tungsten or a tungsten alloy, a liquid mixture of an alkaline solution and hydrogen peroxide can be cited as an example (see, for example, Japanese Unexamined Patent Publication 2001-26890, Japanese Unexamined Patent Publication 2002-25965, Japanese Unexamined Patent Publication 2002-53984 and Japanese Unexamined Patent Publication 2004-31791).
In the case where the etchant contains hydrogen peroxide, however, the composition of the etchant easily changes due to the decomposition of this hydrogen peroxide, and thus, there is a problem with its stability as a chemical. In addition, in the case where an etchant for etching a multilayer film of, for example, a tungsten film and a silicon oxide film is made of only alkaline solutions, there is a problem that the silicon oxide films cannot be etched. Furthermore, the difference in the etching rate between the tungsten film and the silicon oxide film causes a problem where the form after etching becomes poor, the surface of the substrate becomes coarse through etching or etching is carried out unevenly.
Patent Document 1: Japanese Unexamined Patent Publication 2001-26890
Patent Document 2: Japanese Unexamined Patent Publication 2002-25965
Patent Document 3: Japanese Unexamined Patent Publication 2002-53984
Patent Document 4: Japanese Unexamined Patent Publication 2004-31791